Problem: Simplify the following expression: $r = \dfrac{10}{y} \div \dfrac{2}{4y}$
Dividing by an expression is the same as multiplying by its inverse. $r = \dfrac{10}{y} \times \dfrac{4y}{2}$ When multiplying fractions, we multiply the numerators and the denominators. $r = \dfrac{ 10 \times 4y } { y \times 2}$ $r = \dfrac{40y}{2y}$ Simplify: $r = \dfrac{20}{1}$